Electronic devices (typically comprising one or more integrated circuits) are generally subject to a test process in order to verify their correct operation; this is of the utmost importance in order to ensure a high quality of a production process of the electronic devices. The test may be aimed at identifying defects of the electronic devices (each one of them also know as Device Under Test, or DUT) that are either evident or potential, i.e., which might occur after a short period of use. During the test process, the electronic devices may be conditioned thermally (so as to ensure that they work at specific temperatures). A typical example is the burn-in test, wherein the electronic devices are tested under thermal stress conditions by making them working at temperatures being very high or very low (for example, from −50° C. to +150° C.); in this way, it is possible to simulate a long period of operation of the same electronic devices at room temperature (i.e., 25°-50° C.).
The test process may be carried out at wafer level or at package level. In the first case, the integrated circuits are tested directly when they are still comprised in a wafer of semiconductor material; in the second case, instead, the electronic devices are tested after their production is complete (i.e., the integrated circuits have been cut and enclosed into suitable packages). The test at package level reduces the risks of damaging the integrated circuits (for example, due to atmospheric contaminations or hits); moreover, this allows testing the electronic devices in their actual final form.
In the test of the electronic devices at package level, they are assembled onto test boards (for example, a Burn-In Board, or BIB, in case of the burn-in test) that are used for interfacing the electronic devices with a test apparatus. For this purpose, each test board is provided with one or more sockets. Each socket mechanically locks an electronic device and electrically connects its terminals to the test apparatus; at the same time, the socket allows removing the electronic device without any substantial damage at the end of the test process.
The test boards are placed into a global conditioning structure (for example, a oven), and hot or cold air is forced towards them in order to heat or cool, respectively, all the electronic devices mounted thereon. However, in this way the distribution of the temperature throughout the different electronic devices is not uniform.
Therefore, a conditioning element may be provided for each socket, so as to heat or cool the corresponding electronic device locally (in addition to the global action of the hot/cold air or in alternative thereto with the possible addition of a forced ventilation). The conditioning element may also be associated with a temperature sensor, which measures the local temperature of the electronic device so as to allow controlling the conditioning element accordingly.
Generally, the conditioning element is placed on top of the electronic device. However, in this way the electronic device is almost totally shielded from the hot/cold air or the forced ventilation, so that its terminals may reach a temperature that is significantly higher than the one of the package of the electronic device. The high temperature of the terminals (together with the high pressure applied thereto by the socket) may involve metal migration and micro-welding phenomena. These phenomena may deteriorate the socket (thereby adversely affecting its operation), up to damaging it (thereby requiring its replacement with a corresponding waste of time and money). Moreover, in this way the electronic device is to be inserted into and removal from the socket manually (with a deleterious effect on the performance of the test process).
Alternatively, the conditioning element may be arranged so as to act on the bottom of the electronic device.
For example, US-A-2008/0302783 (the entire disclosure of which is herein incorporated by reference) discloses a burn-in board embedding a heating element for each socket; the heating element is formed by a metal trace deposited in a layer of the burn-in board.
US-A-2010/0201389 (the entire disclosure of which is herein incorporated by reference) discloses an integrated unit comprising a heater board and a DUT board in thermal contact therewith; the heater board comprises global and local heaters that are printed thereon, and the DUT board comprises sockets each one in direct physical contact with a local heater.
US-A-2004/0174181 (the entire disclosure of which is herein incorporated by reference) discloses a temperature-controlled system comprising a thermal platform and a thermal plate located under and in thermal communication therewith; a wafer or packaged integrated circuit is mounted on the thermal platform, and a temperature-controlled fluid enters and propagates radially through a porous material of the thermal plate.
US-A-2008/0231309 (the entire disclosure of which is herein incorporated by reference) discloses a performance board comprising a substrate, sockets attached to the substrate and an adiathermic cover member attached to a rear surface of a region of the substrate on which the sockets are mounted.
However, the coupling of each electronic device with the corresponding conditioning element is not entirely satisfactory. Particularly, either the thermal and mechanical features of their assembly may be not completely effective.